The role of manganese and nitrogen nutrition in the susceptibility of wheat plants to take-all in Western Australia

Five field experiments are described which measured the effect of take-all on grain yield of wheat when 5 levels of manganese fertilizer were applied in a factorial combination with 5 different types of nitrogen fertilizer.Ammonium nitrogen fertilizer, either as ammonium sulphate or ammonium chloride, lowered the severity of take-all. By contrast, sodium nitrate had no effect on the incidence and severity of take-all. Ammonium chloride and ammonium sulphate were equally effective at controlling take-all, suggesting that the chloride or sulphate ion had little or no effect on the disease.Manganese sulphate decreased take-all severity at two trial sites. Where manganese was deficient, an application of manganese lowered the severity of take-all, had no effect on the incidence and increased the dry matter and grain yields of the wheat plants. There were no beneficial effects of applied manganese if the wheat plants were adequately supplied with soil manganese.The results suggest that take-all is more severe where plants are deficient in either manganese or nitrogen. The work also suggests that manganese deficiency is not necessarily the reason why the wheat plants grown on the acid soils of south-west Western Australia are prone to take-all.     

Residual value of superphosphate measured using yields of different pasture legume species and bicarbonate — extractable soil phosphorus

The residual value of superphosphate was measured in three glasshouse pot experiments using three different lateritic soils (pH CaCl₂: 4.8–5.3) from south-western Australia. The residual value was estimated relative to levels of freshly-applied superphosphate using yield of dried tops and bicarbonatesoluble P extracted from the soil (soil test values). Up to five successive crops were grown. In each experiment, four different pasture legume species fertilized with mineral nitrogen were grown in rotation with a cereal species. The legume species includedMedicago polymorpha, M. murex, Trifolium subterraneum, Ornithopus compressus, O. perpusillus andO. pinnatus. The cereal species includedTriticum aestivum, ×Triticosecale, andHordeum vulgare. The comparative phosphorus (P) requirement of the different pasture legumes was estimated from the amount of P required to produce 50 or 90% of the maximum yield measured for each species at each harvest. Soil samples for the soil test were collected just before sowing each crop, and were related to the plant yields of that crop.Relative to freshly-applied superphosphate, the residual value of superphosphate measured using plant yield was similar for all pasture legume species, and decreased markedly, by about 50 to 80% between the first and second crop, and by a further 5 to 30% for subsequent crops. The decrease in residual value estimated using soil test values was less marked. For freshly-applied superphosphate, and for the same plant species, the relationship between yield and the level of P applied differed for different crops.There was no consistent, systematic trend for the comparative P requirement of the different legume species within and between crops of the three experiments and soils.For all crops, the relationship between yield of dried tops and P concentration in dried tissue generally differed for the different legume species, indicating the different species usually have different internal efficiency of P use curves. However, for each experiment, when the same cereal species was grown in all the pots, the relationship between yield and P concentration in tissue was similar for previously- and freshly-applied superphosphate, regardless of the pasture legume species grown in previous crops.The relationship between yield and soil test values usually differed, within each crop, for different plant species and for previously- and freshly-applied superphosphate. For the same plant species, the relationship also differed between different crops.     

The effect of zinc fertilizer on take-all and the grain yield of wheat grown on zinc-deficient soils of the Esperance region,Western Australia

Wheat plants were grown in field experiments with five levels of zinc (Zn) fertilizer applied to plots in 1983. The plots were continuously cropped with wheat to allow the build up ofGaeumannomyces graminis var.tritici (Ggt). For experiments 1 and 2, there were high levels of Ggt in the second and third years while for experiment 3 there were high levels of Ggt incidence in the third and fourth year of continuous cropping. The Zn status of the wheat plants, grain yield, and the incidence and severity of take-all were measured for every experiment each year.The Zn-deficient wheat plants were more severely infected by Ggt. However, increasing the Zn supply beyond that required for maximum grain yield had no further effects on decreasing the severity of take-all. The Zn concentration in the youngest emerged blade (YEB) suggested that the Zn status of the wheat plant ranged from severely Zn-deficient through marginal deficiency to sufficiency.The Zn-deficient wheat plant was more susceptible to Ggt infection than Zn-adequate plants. The severity of take-all in the final year was still high in Zn-adequate plants, suggesting high levels of applied Zn (11.2 kg Zn/ha in 1983) had no fungistatic effect on Ggt.     

Residual value of superphosphate for oat and barley grown on a very sandy,phosphorus leaching soil

In a field experiment in a Mediterranean climate (474 mm annual rainfall, 325 mm (69%) falling in the May to October growing season) on a deep sandy soil near Kojaneerup, south-western Australia, the residual value of superphosphate was measured relative to freshly-applied superphosphate. The grain yield of five successive crops (1988–1992) was used to measure the residual value: barley (Hordeum vulgare), barley, oat (Avena sativa), lupin (Lupinus angustifolius), and barley. There was no significant yield response to superphosphate applied to the first crop (barley, cv. Moondyne). There were no results for the second crop (barley) due to weeds or the fourth crop (lupin) due to severe wind erosion which damaged the crop. The residual value of superphosphate was measured using grain yields of the third crop (oat, cv. Mortlock) for superphosphate applied one and two years previously, and the fifth crop (barley, cv. Onslow) for superphosphate applied one, two, three and four years previously. In February 1992, before sowing the fifth crop, soil samples were collected to measure bicarbonate-extractable phosphorus (P) (soil test P) which was related to the subsequent grain yields of that crop. This relationship is the soil test P calibration used to estimate the current P status of soils when providing P fertilizer recommendations.The residual value of superphosphate declined markedly. For the third crop (oat), it was 6% as effective as freshly-applied superphosphate one year after application, and 2% as effective two years after application. For the fifth crop (barley), relative to freshly-applied superphosphate, the residual value of superphosphate in successive years after application was 46%, 6%, 3% and 2% as effective. The soil has a very low capacity to sorb P, and P was found to leach down the soil profile. The largest yield for P applied one and two years previously in 1990, and two, three and four years previously in 1992, was 35 to 50% lower than the maximum yield for freshly-applied P.Soil test P was very variable (coefficient of variation was 32%) and mostly less than 8µg P/g soil. The calibration relating yield (y axis) to soil test P (x axis) differed for soil treated with superphosphate one year previously compared with soil treated two, three and four years previously. The top 10 cm of soil was used for soil P testing, the standard depth. P was leached below this depth but some of the P leached below 10 cm may still have been taken up by plant roots. Consequently soil test P underestimated the P available to plants in the soil profile. The soil test P calibration therefore provided a very crude estimate of the current P status of the soil.     

The effect of water supply on the response of subterranean clover,annual medic and wheat to superphosphate applications

The effect of water supply on the response of subterranean clover (Trifolium subterraneum), annual medic (Medicago polymorpha) and wheat (Triticum aestivum) to levels of phosphorus (P) applied to the soil (soil P) was studied in four glasshouse experiments. P was applied as powdered superphosphate. In one experiment, the effect on plant yield of P concentration in the sown seed (seed P) was also studied. There were two water treatments: the soil was returned to field capacity, by watering to weight, either daily (adequate water, W1) or weekly (water stress, W2). In three experiments: (i) P concentration or content (P concentration × yield) in plant tissue was related to plant yield, and (ii) soil samples were collected before sowing to measure bicarbonate-extractable P (soil test P) which was related to subsequent plant yields.Compared with W1, water stress consistently reduced yields of dried tops and the maximum yield plateau for the relationship between yield and the level of P applied, by up to 25 to 60% in both cases. Compared with W1, the effectiveness of superphosphate for producing dried tops decreased for W2 by 11 to 45%, for both freshly-applied and incubated superphosphate. Consequently in the field, water supply, which varies with seasonal conditions, may effect plant yield responses to freshly — and previously — applied P fertilizer.Seed P increased yields, for W1, by 40% for low soil P and 20% for high soil P; corresponding values for W2 were 20 and 12%. Consequently proportional increases due to seed P were smaller for the water-stressed treatment.The relationship between yield and P concentration or content (internal efficiency of P use) differed for W1 and W2, so that the same P concentration or content in tissue was related to different yields. Estimating the P status of plants from tissue P values evidently depends on water supply, which in the field, differs in different years depending on seasonal conditions.The relationship between yield and soil test P differed for W1 and W2. Predicting yields from soil test P can only provide a guide, because plant yields depend on both P and water supply, which in the field may vary depending on seasonal conditions.     

Effect of defoliation and phosphorus concentration in the sown seed on the response of swards of annual pasture legumes to superphosphate applications

The relationship between dry matter (DM) herbage yield and the level of superphosphate applied to the soil (soil P) was measured for swards of annual pasture legumes in four glasshouse and two field experiments. A single cultivar of one species was used in each experiment. The swards were either uncut, or cut at weekly intervals to a height of 1.5 to 3 cm from the soil surface from about one month after sowing. The sown seeds of each species were of the same size but contained different P concentrations (seed P).For the glasshouse experiments, defoliation reduced DM herbage yields of the species (Trifolium subterraneum, T. balansae, Medicago polymorpha andOrnithopus compressus) by between 20 to 50% two months after sowing, and by 50 to 75% three months after sowing. Higher seed P increased DM herbage yields two months after sowing by about 25% for the lowest soil P level and by 15% for the highest soil P level. Three months after sowing the values were 12 and 8%.In one field experiment, compared with uncut swards, the DM herbage yields for the weekly cut swards ofT. subterraneum were reduced by up to about 5% for the lowest soil P, compared with up to 25% for the highest soil P. Corresponding reductions forM. polymorpha swards in the other field experiment were about 15 and 20%. For the weekly cut swards, high seed P produced large increases in the cumulative DM yields of the weekly cut herbage. Increases for low soil P were about 300% at 2.5 months after sowing and 30% at 4.5 months after sowing. Corresponding values for high soil P were 100 and 20%. However, higher seed P produced only small (zero to 15%) increases in total DM yield of uncut and weekly cut swards (for the weekly cut swards, total DM yield was the cumulative yields of the weekly cut herbage plus the DM yield of the plant residues that were below the cutting height of the mower). Compared with uncut swards, seed production, measured forM. polymorpha only, was reduced by 40% when the swards were regularly cut. Higher seed P increased seed production of uncut swards by 40% for the lowest soil P level and by 25% for the highest soil P level. Corresponding values for the weekly cut swards were 30 and 20%.     

Effectiveness of rock phosphate, coastal superphosphate and single superphosphate for pasture on deep sandy soils

The effectiveness of coastal superphosphate and two rock phosphate fertilizers was compared with the effectiveness of single superphosphate for pasture production on deep, humic, sandy podzols in high rainfall (> 800 mm annual average) areas of south-western Australia. The pastures were subterranean clover (Trifolium subterraneum) or mixed subterraneum clover and serradella (Ornithopus compressus). Coastal superphosphate was made by adding rock phosphate and elemental sulphur to superphosphate during manufacture, as it came out of the den before granulation. One rock phosphate was a 50% mixture of apatite rock phosphate from Nauru and Christmas Islands, and which was also used to make the single and coastal superphosphate used in this study, and superphosphate made in Western Australia at the time these experiments started. The other rock phosphate was Calciphos, the fertilizer produced by heating (calcining), at about 500 °C, Christmas Island C-grade ore, a calcium iron aluminium rock phosphate. There were two types of experiments. In the three Type 1 experiments, levels of each fertilizer were applied annually. In the two Type 2 experiments, levels of fertilizer were applied once only to new plots in different years. Coastal superphosphate was the most effective fertilizer in the Type 1 experiments, with both rock phosphates and single superphosphate being equally effective. All fertilizers were equally effective in the Type 2 experiments. There were large variations in fertiliser effectiveness values between yield measurements in the same or different years. It is known that P leaches from freshly-applied superphosphate in these soils. The extent of this leaching probably varies between yield measurements affecting effectiveness values determined for all fertilizers because the effectiveness values were calculated relative to the effectiveness of single superphosphate. The humic, sandy podzols remain wet during the growing season, are acidic, and are known from laboratory studies to possess adequate hydrogen ions to cause extensive dissolution of North Carolina rock phosphate so that rock phosphates are equally or more effective than single superphosphate in these soils. When elemental sulphur in coastal superphosphate is oxidized to SO₄ hydrogen ions are produced which in previous studies has been shown to enhance dissolution of rock phosphate in biosuper, a mixture of rock phosphate and elemental sulphur.     

Nitrogen fertigation of greenhouse-grown strawberries

Two greenhouse experiments were conducted with strawberries (Fragaria ananassa) grown in plastic pots filled with 12 kg of soil, and irrigated by drip to evaluate the effect of 3 N levels and 3 N sources. The N levels were 3.6, 7.2 or 10.8 mmol Nl^–1 and the N sources were urea, ammonium nitrate and potassium nitrate for supplying NH₄/NO₃ in mmol Nl^–1 ratios of 7/0, 3.5/3.5 or 0/7, respectively. Both experiments were uniformly supplied with micronutrients and 1.7 and 5.0 mmoll^–1 of P and K, respectively. The fertilizers were supplied through the irrigation stream with every irrigation. The highest yield was obtained with the 7.2 mmol Nl^–1 due to increase in both weight and number of fruits per plant. With this N concentration soil ECe and NO₃-N concentration were kept at low levels. Total N and NO₃-N in laminae and petioles increased with increasing N level. With the N sources the highest yield was obtained with urea due to better fruit setting. The N source had no effect on soil salinity and residual soil NO₃-N; residual NH₄-N in the soils receiving urea and ammonium nitrate were at low levels.     

Incorporation of nitrification inhibitors with urea and urea-ammonium nitrate for irrigated corn

Nitrapyrin [2-chloro-6-(trichloromethyl)pyridine] has been shown to delay nitrification and may increase nitrogen (N) utilization efficiency of crops under N loss conditions. Current application recommendations suggest immediate incorporation. With fertilizer N sources such as urea and urea-ammonium nitrate (UAN) solution, immediate incorporation may not be practical. Experiments were conducted with irrigated corn (Zea mays L.) over 3 years to determine if nitrification inhibitor (NI) incorporation and contact with the fertilizer source was essential with urea and UAN to maintain efficacy of nitrapyrin and etridiazol [5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole]. Nitrogen at a rate of 134 kg ha^–1 was broadcast on a Hubbard loamy coarse sand (sandy, mixed Udorthentic Haploboroll) before planting. Nitrification inhibitors were applied at 0.56 kg ha^–1 either as coating on urea, mixed with UAN, or applied in a broadcast application separate from the application of the N fertilizer. Incorporation was conducted immediately after NI application. Leaching losses, reduced N availability each year of experimentation. Nitrogen uptake from urea with no NI applied was 26% higher than uptake from UAN and resulted in 11% higher grain yields. Volatilization of urea from either N source was not apparent. Nitrapyrin and etridiazol produced similar increases in N utilization and yield. Incorporation of nitrapyrin and etridiazol was essential to obtain efficacy with both fertilizer sources. Incorporation of both NIs (averaged over NI) increased grain yields 28% with urea and 16% with UAN. Separate applications of NI provided comparable results to application with the fertilizer material if the NI was incorporated immediately.Journal Paper No. 16074 Univ. of Minnesota Agric. Expt. Sta., St. Paul, MN 55108. Contribution from the Department of Soil Science. This work was supported in part by Dow Chemical U.S.A. and the Olin Corp.     

Post-establishment phosphatic fertilizer treatments in a New South WalesPinus radiata plantation

A five-year-oldPinus radiata plantation treated with a spot application of phosphatic fertilizer (13.5 g P per tree)(23 kg P ha^–1) at planting was given various additional booster treatments: two levels of superphosphate (48 and 72 kg P ha^–1) and one level each of basic superphosphate (61 kg P ha^–1) and monoammonium phosphate (70 kg P ha^–1, 35 kg P ha^–1) all broadcast applied. All fertilizer treatments resulted in significant increases in timber volume production which were not significantly different from each other. The stands which had received no additional treatment produced 108 m³ ha^–1 merchantable timber at age 17 years while the treated plots produced between 188 and 201 m³ ha^–1. The best financial gains were from the higher rate of superphosphate. The experiment is discussed in relation to foliar analysis and routine management practice.     

Nitrogen-15 and sulfur-35 balances for fertilizers applied to transplanted rainfed lowland rice

A field experiment was conducted on a poorly-drained Aeric Paleaquult in northeastern Thailand to determine the effect of N and S fertilizers on yield of rainfed lowland rice (Oryza sativa L.) and to determine the fate of applied¹⁵N- and³⁵S-labeled fertilizers. Rice yield and N uptake increased with applied N but not with applied S in either sulfate or elemental S (ES) form. Rice yield was statistically greater for deep placement of urea as urea supergranules (USG) than for all other N fertilizer treatments that included prilled urea (PU), urea amended with a urease inhibitor (phenyl phosphorodiamidate), and ammonium phosphate sulfate (16% N, 8.6% P).The applied¹⁵N-labeled urea (37 kg N ha^–1) not recovered in the soil/plant system at crop maturity was 85% for basal incorporation, 53% for broadcast at 12 days after transplanting (DT), 27% for broadcast at 5–7 days before panicle initiation (DBPI), and 49% for broadcast at panicle initiation (PI). The basal incorporated S (30 kg ha^–1) not recovered in the soil/plant system at crop maturity was 37% for sulfate applied as single superphosphate (SSP) and 34% for ES applied as granulated triple superphosphate fortified with S (S/GTSP). Some basal incorporated¹⁵N and³⁵S and some broadcast¹⁵N at PI was lost by runoff. Heavy rainfall at 3–4 days after basal N incorporation and at 1 day after PI resulted in water flow from rice fields at higher elevation and total inundation of the 0.15-m-high¹⁵N and³⁵S microplot borders. Unrecovered¹⁵N was only 14% for 75 kg urea-N ha^–1 deep placed as USG at transplanting. This low N loss from USG indicated that leaching was not a major N loss mechanism and that deep placement was relatively effective in preventing runoff loss.In order to assess the susceptibility of fertilizer-S to runoff loss, a subsequent field experiment was conducted to monitor³⁵S activity in floodwater for 42 days after basal incorporation of SSP and S/GTSP. Maximum³⁵S recoveries in the floodwater were 19% for SSP after 7 days and 7% for S/GTSP after 1 day. Recovery of³⁵S in floodwater after 14 days was 12% for SSP and 3% for S/GTSP.This research suggests that on poorly drained soils with a low sorption capacity, a sizeable fraction of the fertilizer S and N remains in the floodwater following application. Runoff could then be an important mechanism of nutrient loss in areas with high probability for inundation following intense rainfall.     

Yield and soil nutrient balance of a sugarcane plant–ratoon system with conventional and organic nutrient management in sub-tropical India

A 3-year field trial of sugarcane, comprising 11 treatment combinations of different organic manures with and without Gluconacetobacter diazotrophicus (Gd), NPK and an absolute control, on an inceptisol was conducted to assess the effect of these treatments on sugarcane total and economic yield, the benefit:cost ratio, nutrient balance and soil quality in a sugarcane plant–ratoon system. The highest cane yield (78.6 t ha⁻¹) was recorded in the plant crop given vermicompost + Gd, whereas ratoon yields (first and second) were highest (80.8 and 74.9 t/ha⁻¹, respectively) with sulphitation press mud cake (SPMC) + Gd. In both plant and ratoon crops, a number of different organic manures produced the highest cane yield that was also statistically similar to those obtained with using the recommended NPK levels (76.1, 78.2 and 71.7 t/ha for plant crop and subsequent two ratoons, respectively). The highest benefit:cost (B:C) ratio in the plant and two ratoon crops (1.28, 2.36, 2.03 respectively) were obtained with the addition of SPMC + Gd. The nutrient balance for NPK in the soil was highest in the SPMC + Gd treatment. The highest increase in organic C (94%) and total N (87%), in comparison to the initial level, and soil microbial biomass C (113%) and soil microbial biomass N (229%), in comparison to the control treatment, was recorded with the addition of SPMC + Gd. The maximum decrease in soil bulk density (BD) (12%) with an increase in soil aggregate (17%) and water infiltration rate (35%) was obtained with the addition of SPMC. Overall, the sugarcane crop responded well to different organic manures in a multiple ratooning system with a better economic output and improved soil quality. Strategic planning in terms of an integrated application of these manures with inorganic chemicals will not only sustain our soils but will also be beneficial for our farmers in terms of reducing their dependence and expenditure on chemical fertilizers.     

A comparison between legume technologies and fallow, and their effects on maize and soil traits, in two distinct environments of the West African savannah

Legume–maize rotation and maize nitrogen (N)-response trials were carried out simultaneously from 1998 to 2004 in two distinct agro-ecological environments of West Africa: the humid derived savannah (Ibadan) and the drier northern Guinea savannah (Zaria). In the N-response trial, maize was grown annually receiving urea N at 0, 30, 60, 90 and 120 kg N ha⁻¹. In Ibadan, maize production increased with N fertilization, but mean annual grain yield declined over the course of the trial. In Zaria, no response to N treatments was observed initially, and an increase in the phosphorus (P) and sulphur (S) fertilizer application rate was required to increase yield across treatments and obtain a response to N applications, stressing the importance of non-N fertilizers in the savannah. In the rotation trial, a 2-year natural fallow–maize rotation was compared with maize rotated with different legume types: green manure, forage, dual-purpose, and grain legumes. The cultivation of some legume types resulted in a greater annual maize production relative to the fallow–maize combination and corresponding treatments in the N-response trial, while there was no gain in maize yield with other legume types. Large differences in the residual effects from legumes and fallow were also observed between sites, indicting a need for site-specific land management recommendations. In Ibadan, cultivation of maize after the forage legume (Stylosanthes guianensis) achieved the highest yield. The natural fallow–maize rotation had improved soil characteristics (Bray-I P, exchangeable potassium, calcium and magnesium) at the end of the trial relative to legume–maize rotations, and natural fallow resulted in higher maize yields than the green manure legume (Pueraria phaseoloides). In Zaria, maize following dual-purpose soybean achieved the highest mean yield. At both sites, variation in aboveground N and P dynamics of the legume and fallow vegetation could only partly explain the different residual effects on maize.     

Long-term residual value of North Carolina and Queensland rock phosphates compared with triple superphosphate

The effectiveness of large single applications of North Carolina reactive rock phosphate, Queensland non-reactive rock phosphate, and Calciphos, were compared to the effectiveness of superphosphate in field experiments in south-western Australia for up to 11 years after application. As measured using plant yield, superphosphate was the most effective fertilizer in the year of application, and relative to freshly-applied superphosphate, the effectiveness of the superphosphate residues declined to be about 15 to 65% as effective in the year after application, and 5 to 20% as effective 9 to 10 years after application. Relative to freshly-applied superphosphate, all the rock phosphates were 10 to 30% as effective in the year of application, and the residues remained 2 to 20% as effective in the 10 years after application. The bicarbonate soil test reagent predicted a more gradual decrease in effectiveness of superphosphate of up to 70% 10 years after application. For rock phosphate, the reagent predicted effectiveness to be always lower than for superphosphate, being initially 2 to 11% as effective in the year after application, and from 10% to equally as effective 10 years later. Therefore rock phosphates are unlikely to be economic alternatives to superphosphate in the short or long term on most lateritic soils in south-western Australia.     

Effect of water supply on the response of wheat and triticale to applications of rock phosphate and superphosphate

The effect of water supply on the response of wheat (Triticum aestivum) and triticale (×Triticosecale) to levels of freshly-applied rock phosphate and superphosphate, and the residues of these fertilizers applied 9 years previously in the field, was studied in three glasshouse experiments. The < 2 mm fraction of the top 10 cm of soil was used (1.8 kg soil per pot), and in one experiment, freshly-applied fertilizer was also added to the more acidic subsoil (10 to 20 cm). There were two water treatments: the soil was returned to field capacity by watering to weight, either daily (W1, adequate water) or weekly (W2, water stress). Yield of dried tops was used to calculate fertilizer effectiveness. The phosphorus (P) concentration in dried tops was used to determine critical P, which is the P concentration related to 90% of the maximum yield. Just before sowing, soil samples were collected to measure bicarbonate-extractable (soil test) P which was related to plant yield.Water stress reduced yields and maximum yield plateaus by 20 to 40%. Water stress reduced the effectiveness of all P fertilizers by between 20 to 60%, largely because of a reduction in the maximum yield potentials. In the field, water supply is seasonally dependent and it can affect the yield response of plants to freshly-applied rock phosphate and superphosphate and the residues of these fertilizers applied to the field in previous years. Relative to placing fertilizer in the topsoil, placing fertilizer in the subsoil improved effectiveness by about 26% for rock phosphate and 12% for superphosphate.The relationship between yield and P concentration in dried tops, and critical P, differed for W1 and W2. The soil test P calibration, which relates yield to soil test P, and the soil test P required to produce the same yield also differed for W1 and W2. Consequently critical P and soil test P calibrations depend on water supply, which in the field varies within and between growing seasons. This is so for freshly- and previously-applied rock phosphate and superphosphate.     

Effect of nitrification inhibitors on herb and essential oil yield of Japanese mint on sandy soil

Pyrethrum (Chrysanthemum cinerariefolium) flowers have been observed to have insecticidal properties and could be used as an indigenous nitrification inhibitor for increasing N-use efficiency. A field experiment was conducted at the Central Institute of Medicinal and Aromatic Plants, Lucknow, India during 1988 and 1989 to evaluate the relative performance of pyrethrum flower waste and Dicyandiamide (DCD) as nitrification inhibitors applied with prilled urea (PU) to Japanese mint (Mentha arvensis L.). The results revealed that application of the nitrification inhibitors with prilled urea significantly increased the herb and essential oil yield of the crop compared to that of prilled urea alone. Addition of Dicyandiamide and pyrethrum flower waste gave 30 and 23% more herb yield than prilled urea alone, the corresponding increase in oil yield being 27 and 22%, respectively. Application of nitrogen at 200 kg ha^–1 in dicayndiamide or pyrethrum flower waste treated soil significantly enhanced the herb and essential oil yields and N-uptake by the crop to more than that for 300 kg N ha^–1 with prilled urea. Both the materials improved the N use efficiency by one and half time as compared to that with PU at 100 kg N ha^–1. The results indicate pyrethrum flower dust can be effectively used as a potential nitrification inhibitor.     

Sucrose fatty acid esters enhance efficiency of foliar-applied urea-nitrogen to soybeans

A greenhouse study is described showing the effect of sucrose fatty acid esters (SFE) applied to soybeans (Glycine max (L.) Merrill cv Fukuyutaka) during the flowering and/or pod-filling periods on the efficiency of foliar-applied urea-nitrogen. SFE applied in combination with urea delayed senescence and when applied during both the flowering and pod-filling periods increased seed yields by 103% and nitrogen accumulation by 132% as compared to urea alone. Average total recovery of¹⁵N-urea in the above ground portions of the plant was 20.6%. SFE combined with urea increased the average recovery to 34.8%. Recovered¹⁵N-urea was only a small portion of the total nitrogen content of the plant. The yield increase resulting from a foliar application of urea may have been due to the leaves continuing to export photosynthates to the nodules hence maintaining the nodules' nitrogen fixing activity for a longer period of time. The addition of SFE to the urea solution increased the retention and/or absorption of urea and increased translocation of urea-nitrogen to the seeds.     

Response of rainfed bread and durum wheat to source,level and timing of nitrogen fertilizer on two Ethiopian Vertisols: II. N uptake,recovery and efficiency

In trials conducted at 2 highland Vertisol sites in Ethiopia in 1990 and 1991, 2 locally popular wheat cultivars, 1 spring bread wheat (Triticum aestivum L.) and 1 durum wheat (T. durum Desf.), were supplied with nitrogen (N) fertilizer at 0, 60 and 120 kg N ha^–1 in the form of large granular urea (LGU), standard urea prills or ammonium sulfate. N was applied all at sowing, all at mid-tillering or split-applied between these two stages (1/3:2/3). While durum wheat exhibited the highest N concentration in grain and straw, bread wheat, because of its higher productivity, resulted in a greater grain and total N uptake. In general, split application of N and use of LGU as N source enhanced grain and total N uptake, apparent N recovery and agronomic efficiency of N, particularly under severe water-logging stress. Where significant, the interactions among the experimental factors substantiated the superior responsiveness of the bread wheat cultivar to fertilizer N, and the beneficial effects of split N application and LGU as an N source. Split application of N tended to nullify the positive effects of LGU, presumably by approximating the delayed release of N achieved with LGU. Considering the potential benefits to Ethiopian peasant farmers and consumers, split application of N should be advocated, particularly on water-logged Vertisols; LGU could be an advantageous N source assuming a cost comparable to the conventional N source urea.     

Effect of urea and salt on micelle formation of zwitterionic surfactants

The effect of urea on micelle formation of zwitterionic surfactants was investigated by measuring conductivity, critical micelle concentration (CMC), relative viscosity, and the spectrophotometric shift in wavelength. We examined two zwitterionic surfactants, N,N-dimethyl dodecylamine N-oxide and N,N-dimethyl tetradecylamine N-oxide (DMTAO). The CMC values of the surfactants increased with the addition of urea. Also, the relative viscosity of the surfactant solutions decreased at higher concentrations of urea and increased with increasing KCl concentration. The absorbance maxima of the surfactants decreased with increasing urea concentration.     

Effect of phosphate rock and triple superphosphate on soil phosphorus fractions and their plant-availability and downward movement in two volcanic ash soils under <Emphasis Type="Italic">Pinus radiata</Emphasis> plantations in New Zealand

Changes in phosphorus (P) fractions and their plant-availability and downward movement in two strongly P fixing acidic Andosols (Allophanic and Pumice Soils) under Pinus radiata plantations in New Zealand were studied 2 years after triple superphosphate (TSP) and a phosphate rock (BGPR, origin Ben Guerir, Morocco) application, each at four rates, to determine the fate and plant availability of fertilizer-derived P in these soils. The rate of increase of the concentrations of the P fractions was highest for NaOH-P_i (inorganic P associated with Fe and Al oxides and allophane) when TSP was applied and highest for H₂SO₄-P_i (predominantly calcium phosphates or apatite-type P minerals) when BGPR was applied. The largest pool of soil P, the NaOH-P_o (labile organic P), was unaffected by the P fertilizer applications. The rate of NaOH-P_i concentration increase was higher in the higher P fixing Allophanic Soil than in the Pumice Soil. Both types of fertilizers increased resin-P_i (Inorganic P freely available to the plant) and Bray-2 P concentrations but only the TSP application increased Olsen P concentration. Phosphorus derived from TSP and BGPR applications moved down to 10–20 cm soil depth within 2 years of application in the Pumice Soil, but did not move below 10 cm depth in the higher P fixing and less porous Allophanic Soil. The fertilizers significantly increased needle P concentrations 2, 3 and 4 years after fertilizer application, but did not have any significant effect on tree growth.